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Method for producing polyethylene

a polyethylene and polyethylene technology, applied in chemical/physical/physical-chemical stationary reactors, chemical apparatus and processes, chemical/physical/physical-chemical processes, etc., can solve the problems of significant downtime of the reactor, ineffective cost-effective cleaning operations, and time-consuming cleaning operations, so as to avoid equipment cleaning, increase the melt flow index, and reduce the effect of downtim

Active Publication Date: 2013-05-23
TOTAL RES & TECH FELUY
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The invention is about a new method for producing different polyethylene products in the same polymerization and processing line without the need for cleaning or purging. This improves the efficiency and cost-effectiveness of the process. The method involves producing the first polyethylene resin using a Ziegler-Natta or Chromium catalyst and then producing the second polyethylene resin using a metallocene catalyst. The ratio of the melt flow index of the first polyethylene resin to the second polyethylene resin is at least 0.3. This allows for the use of polymers with higher melt flow indices subsequently without the need for equipment cleaning.

Problems solved by technology

If not removed, this material, subject to the heat of the extrusion process, degrades over time and can contaminate fresh polymer passing through the extrusion apparatus.
This work is not only very demanding in terms of labour, but also results in a significant down time of the reactor while cleaning operations are performed as cleaning procedures include extensive flushing of the reactor pipes, extensive physical effort with brushes, detergent and water, or even entirely reactor dismantling.
Therefore, cleaning operations not only are time-consuming, but also are cost-ineffective.

Method used

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Examples

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example 1

[0082]Two different polyethylene resins were consecutively produced in the same slurry loop reactor: the first polyethylene resin was produced in the presence of a Ziegler-Natta catalyst (ZN). The melt flow index MI2 of the ZN produced polyethylene resin was 0.7 g / 10 min. At the end of the ZN run and after catalyst shift procedure (consisting in killing, emptying and conditioning the reactor), a second polyethylene resin was consecutively produced in the same reactor in the presence of a metallocene catalyst. MI2 of the metallocene produced resin was 8 g / 10 min. The ratio of the MI2 of the ZN produced resin to the MI2 of the metallocene produced resin was 0.09.

[0083]The resins were consecutively extruded. The gel level was measured in the extruded pellets as ppm as a function of time.

[0084]The gels level measured in the extruded resins are shown in FIG. 2A. High level of gels was observed during about 3 days. The specification of the resin was finally corrected thanks to contaminati...

example 2

[0085]Two different polyethylene resins were consecutively produced in one slurry loop reactor: a first polyethylene resin with a MI2 of 0.9 g / 10 min was produced in the presence of a Ziegler-Natta catalyst. At the end of the ZN run and after catalyst shift procedure (consisting in killing, emptying and conditioning the reactor), a second polyethylene resin with a MI2 of 8 g / 10 min was consecutively produced in the same reactor in the presence of a metallocene catalyst. The ratio of the MI2 of the first produced polyethylene resin to the MI2 of the second produced polyethylene resin was 0.11.

[0086]The resins were consecutively extruded. The gel level was measured in the extruded pellets as ppm as a function of time.

[0087]The gels level measured in the extruded resins are shown in FIG. 2B. High level of gels was observed during about 4 days. The specification of the resin was finally corrected thanks to contamination dilution with time and production of resins with an MI2 of 0.9.

example 3

[0088]Two different polyethylene resins were consecutively produced in one slurry loop reactor: A first polyethylene resin with a MI2 of 7.5 g / 10 min was produced in the presence of a Ziegler-Natta catalyst. At the end of the ZN run, and in the same reactor, a second polyethylene resin with a MI2 of 0.9 g / 10 min was consecutively produced in the presence of a metallocene catalyst. The ratio of the MI2 of the first produced polyethylene resin to the MI2 of the second produced polyethylene resin was 8.3.

[0089]The resins were consecutively extruded. The gel level was measured in the extruded pellets as ppm as a function of time. The results are shown in FIG. 3A. As shown in the figures no off grades (OG) was observed. The present inventors have shown that gels problem could be controlled. This was achieved by making sure that the melt flow index ratio between the first and the second polyethylene product was at least 0.3.

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Abstract

The present invention relates to a method for consecutively producing at least two different polyethylene resins in one slurry loop reactor, comprising producing a first polyethylene resin in the presence of a Ziegler-Natta and / or a Chromium catalyst, and consecutively producing a second polyethylene resin in the presence of a metallocene catalyst, characterized in that the ratio of the melt flow index of the first produced polyethylene resin to the melt flow index of the second produced polyethylene resin is at least 0.3.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates to the field of producing polyethylene. In particular, the invention relates to a process for the sequential production of polyethylene in a slurry loop reactor. More in particular the invention relates to a process for the consecutive production of polyethylene having different properties in a slurry loop reactor.BACKGROUND OF THE INVENTION[0002]Polyolefins, such as polyethylene (PE), are synthesized by polymerizing olefin, such as ethylene (CH2=CH2), monomers. Because it is cheap, safe, stable to most environments and easy to be processed polyethylene polymers are useful in many applications. According to the properties polyethylene can be classified into several types, such as but not limited to LDPE (Low Density Polyethylene), LLDPE (Linear Low Density Polyethylene), and HDPE (High Density Polyethylene). Each type of polyethylene has different properties and characteristics.[0003]Olefin polymerizations are frequ...

Claims

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Application Information

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IPC IPC(8): C08F2/01
CPCB01J8/226B01J19/1837B01J2219/00006C08F210/16C08F2410/03C08F2/01C08F2/14C08F210/14C08F2500/24C08F2500/05C08F2500/12B01J19/18C08F2/02C08F4/00C08F10/02
Inventor STEVENS, PETERFANT, FRANKYDEWACHTER, DAANBRUSSELLE, ALAIN
Owner TOTAL RES & TECH FELUY
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